1. Copyright Authorization
A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by any one of the patent disclosure, as it appears in the U.S. Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever.
2. Field of the Invention
The field of the present invention relates in general to a system and method for processing commands and transferring data in a computer system. More particularly, the field of the invention relates to a system and method for processing sound I/O commands and transferring sound data or the like across a high speed bus.
3. Background
Personal computers and work stations have evolved rapidly since their introduction nearly twenty years ago. Dramatic advances in processor, display and audio technology have transformed the personal computer into a multimedia appliance, capable of combining color graphics, video, and stereo sound in a single application.
As multimedia applications have developed, there has been an increased need for high speed and high bandwidth data transfers between main memory and input/output (I/O) devices. One approach used in expansion bus systems is direct memory access (DMA). A DMA controller takes over the bus and transfers data without intervention by the central processing unit (CPU). This method of data transfer has become prevalent for sound cards attached to an ISA expansion bus, and there is a large installed base of software applications designed for these sound cards.
However, data transfer across conventional expansion buses has not been able to keep pace with the demands of graphics and video systems used with modem multimedia software applications. Rather, graphics and video systems are increasingly being attached to the local bus where burst mode block data transfer initiated by the CPU supports higher data transfer rates than conventional DMA systems. In addition, local buses typically have a wider data path than expansion buses. However, local buses, such as the VESA local bus and the PCI bus, typically do not provide connections to the DMA controller.
Therefore, conventional sound systems and other systems requiring DMA are incompatible with these high speed local bus systems, and have remained on the expansion bus. It is a disadvantage of these systems that they are unable to take advantage of the higher data transfer rates of local bus systems. This has also led to the development of separate graphics, video, and audio subsystems on different buses having independent controllers with incompatible data types. This may lead to wasted memory space and memory bandwidth, duplicated bus interface logic, and wasted CPU cycles to manage independent subsystems.
What is needed is a system and method for emulating conventional DMA transfers while taking advantage of higher rates provided by other modes of transferring data.
What is also needed is a sound system that uses high speed data transfer while maintaining compatibility with the extensive installed base of software applications written for conventional sound systems. Preferably such a system would allow sound data to be transferred across a bus at a high rate of speed to free up bus bandwidth for video and graphics, yet would allow sound data to be played or recorded at a conventional lower frequency. What is also needed is a multimedia system that combines graphics, video, and audio in a single subsystem attached to the local bus or some other high speed I/O bus.